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Spatial resolution tests of scanning auger microscopy under different topographical conditions

: Umbach, A.; Hoyer, A.; Brünger, W.H.

Surface and Interface Analysis 14 (1989), pp.401-406
ISSN: 0142-2421
Journal Article
Fraunhofer ISIT ()

Highly focused electron beams have been scanned across chemical edges of different surface structures in a scanning Auger microscope with a field emission gun. For the case of a fracture plane across a multilayer structure with 100 nm Ta and 100 nm Si layers, a resolution of 35 nm for the Ta signal was found. In contrast to these flat samples, analytical problems in semiconductor technology require analysis of submicrometre features with high aspect ratios. Under these conditions, the scanning Auger microscopy (SAM) resolution is drastically affected by electron scattering. To study these effects, we used x-ray mask structures consisting of 0,6 mym high Au on Si (100) fabricated by x-ray lithography. We scanned over a heterogeneous step of this kind with the three different electron beam energies 10, 20 and 30 keV and measured the lateral intensity distribution of the Si signal. This signal does not stop at the edge but extends into the gold plane over a distance that increases with be am energy as expected. When analysing small features, this effect leads to a misinterpretation of the Auger spectra. This problem becomes more severe as the feature size is reduced. This has been demonstrated for gold bars of different widths and different sized columns. To minimize the contribution of nearby regions to the spectrum, the lowest beam voltage is recommended, which is sufficient to achieve the required beam diameter.